It has been known that organic materials such as thermoplastic resin, thermosetting resin, natural or synthetic rubber, mineral oil, lubricating oil, adhesive or paint are deteriorated by an action of heat, oxygen, etc. on their production, processing and use to cause lowering of the strength of the organic materials, change in flow properties, coloring, deterioration of surface physical properties due to a phenomenon such as molecular cleavage or molecular closslinking. These deterioration result in decrease of their commercial value. It has hitherto been known that the organic material is stabilized by various phenol and phosphorous antioxidants, and these antioxidants have been used for solving problems of heat deterioration and oxidation deterioration.
As the phosphorous antioxidant, for example, distearyl pentaerythritol diphosphite, tris(2,4-di-t-butylphenyl)phosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite and bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite are used.
However, the stabilizing effect to heat deterioration and oxidation deterioration of these known phosphorous antioxidants is insufficient. For example, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite and the like had a problem that, since it is liable to be hydrolyzed, the hydrolysis occurs on storage to cause scattering in processing stability and an organic material having stable quality can not be obtained, and a problem that a metal in a processing machine is corroded by phosphites produced as a result of the hydrolysis.
On the other hand, for solving the problem of the known phosphorous antioxidants, the present inventors have already suggested a cyclic phosphite having a carbonyloxyalkylene group, such as 2,10-dimethyl-4,8-di-t-butyl-6-{2-3-(3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy!ethoxy}-12H-dibenzod,g!1,3,2!dioxaphosphosine. (JP-A-5-86084).
However, although the stabilizing effect of this cyclic phosphite to heat deterioration and oxidization deterioration was improved, this improvement was still not satisfactory. The coloring resistance of this cyclic phosphite to a NOx gas is not sufficient either. Therefore, more improvement has been desired.
The present inventors have produces various cyclic phosphites and studied intensively so as to develop the phosphorous compound which hardly cause the hydrolysis and the stabilizing effect to heat and oxidization deterioration and NOx gas has been improved. As a result, it has been found that specific cyclic phosphites having a carbonyl group or an alkylene group in place of the carbonyloxyalkylene group shows excellent stabilizing effect. Thus, the present invention has been accomplished.